This invention relates to an improved compact photometer primarily intended for use by individual scientists or physicians having limited laboratory space for conducting tests away from the laboratory (i.e. in the field).
The improved photometer of this invention is equipped with a novel automatic centering device.
The advent of such testing procedures as the Enzyme-Linked Immunosorbent Assay (ELISA) has come into widespread use in a growing number of laboratories engaged in the determination of immunologic parameters. This analytical ELISA test is performed by taking Colorimetric readings in microtiter plates. Although visual observation of the color changes (eyeballing) in the test is sometimes practiced, a much higher degree of accuracy can be achieved by reading the test in a microphotometer.
Recent attempts have been made to design colorimeters (photometers) which permit the direct measurement of microplates in enzyme immunoassay systems. Although some progress has been made in this area the devices designed to measure optical density in microtiter plates date have been very expensive. One problem in designing a colorimeter capable of making optical desity determinations in a microtiter plate is that each well must be identically aligned with the optical system. Otherwise there will be variation in the readings due to refractive differences.
The article by Thomas R. Clem et al, Journal of Clinical Microbiology, "Practical Colorimeter for Direct Measurement of Microplates in Enzyme Immunoassay Systems", Vol. 7, No. 1, January 1978, pages 55-58 describes a colorimeter in which the microtiter tray fits into a carrier that can be located at any of the 96 position wells of the microtiter tray in the path of the optical system.
U.S. Pat. No. 3,441,352 discloses a colorimeter having a plurality of photoelectric cells, each having associated with it a light filter which removes all except the particular monochromatic band of light to which the photoelectric cell is primarily responsive and where its peak response is located.
U.S. Pat. No. 3,489,525 discloses a colorimeter which measures out a test sample of the order of about 1 to 100 microliters, divides this sample into as many aliquots of test solution as desired and then analyzes each one individually and simultaneously using a revolving turntable mechanism for positioning the test samples.